Well, the current move toward a pay-as-you-go computing model seems to bring the industry full circle. As the computer industry moves away from pushing new hardware onto business users, the SOA (service-oriented architecture) model has begun to evolve as a preferred model for providing compute services to the business world.
This isnt a sudden emergence; major software vendors such as Sun Microsystems and Microsoft for years have been touting the "service" aspect of their products (and sounding suspiciously like IBM mainframe salesmen from the 1960s).
But what has happened is that the enabling technologies—which involve the ability to deliver a service-based model of computing without requiring dedicated, proprietary hardware, networking or communications—have become commonplace, and the service-oriented vendors now find themselves with a fertile field to plant their concepts.
But to businesses that chose to use this model, it means a return to the days of single-vendor computing environments. While its one thing to add a specific service to your computing environment, when you approach the issue by placing your key business processes in the hands of service vendor, you wont be doing anything that is likely to disrupt that service.
This means that the service provider will, at best, become the general contractor for your IT efforts, signing off on your IT choices to guarantee that these choices dont disrupt your line of business applications.